An electrocardiogram (ECG) is a very important tool in the diagnosis of heart disease and abnormalities in both children and adults. The new signal processing and detection capabilities provided when using maternal abdominal ECG electrodes provides access to the ECG of unborn children. The use of a fetal ECG (fECG) can lead to the early detection and monitoring of heart abnormalities that can be treated, which in turn leads to better fetal health.
However, obtaining an accurate fetal ECG is difficult due to the weaker fetal electrical signals obtained from the abdomen of the mother. Specifically, when multiple ECG electrodes are placed on the abdomen of the mother to gather the required ECG information, several obvious problems arise. The first is that the mother's ECG is present and is usually significantly larger than the ECG of the fetus. Second, if monitoring is being done late in pregnancy, uterine contractions may be present, which result in large electrical artifacts that obliterate or mask the fetal signal. Third, in many cases, the mother is experiencing discomfort and is unable to lie still, which creates large electrical muscle artifacts.
Presently, signal processing techniques exist, including the use of independent component analysis (ICA) algorithms that can be applied to the input ECG signals obtained from the mother to provide clean waveforms that can be further processed. The output signals from the ICA algorithm can be further processed to provide information relating to the maternal and fetal heart rate, maternal and fetal ECG intervals, and uterine contraction intensity and episodes. In application, the input signals to the ICA algorithm contain combinations of the signals from these various sources. The purpose of the ICA is to separate these sources so that the desired information about each source can be identified. The output of the ICA algorithm will provide at least one channel waveform for each source. Typically, the ICA algorithm is performed using the entire set of input channels over an epoch having a pre-determined time duration, such as 4-5 seconds. Although ICA algorithms can separate fetal ECG, maternal ECG, and uterine waveforms for a specific epoch, the ICA algorithms must be conducted over an epoch having a specific period. Therefore, for example, the fetal ECG information and waveform displayed on a monitor represents the ECG information and waveform for the fetus over the previous epoch. Since the ICA algorithm requires input waveforms recorded over an epoch to calculate the output ICA waveforms, the ECG information derived for a fetus is delayed prior to display. Further, the ICA algorithm does not guarantee that the output signal associated with a particular source is on the same ICA output channel from epoch to epoch Therefore, a need exists to provide for continuous display of the fetal ECG information and waveform without requiring the delay period of the epoch and without requiring channel sorting for each new ICA epoch output. This means that a method of processing an epoch, at least temporarily during its acquisition, would be useful. After an epoch is completely obtained it can be further processed as usual to optimize source separation and channel sorting before moving on to subsequent epochs for display and monitoring.